The technical field of this invention concerns methods and apparatus for optically detecting the presence of fluids and, in particular, sensors for detecting undesirable fluids, such as hydrocarbons, if present in an ambient environment.
The detection and measurement of hydrocarbon fluid leaks and ground water contaminants, generally, is of considerable present interest. It is of particular interest to monitor the integrity of tanks containing potential environmental pollutants. For example, gasoline and oil tanks can cause severe contamination of the local environment, if such tanks or associated pipelines begin to leak. Moreover, when a dispenser of such fuels, such as typically found in a gasoline service station, is leaking, there is potential not only for environmental harm but also fires, explosions or other safety hazards.
Since it is usually impracticable to conduct manual or visual inspections of buried storage tanks and the inner pans or sumps of dispensing equipment, various sensor systems have been devised. For underground gasoline storage tanks, bore holes are typically drilled into the ground at various locations around the perimeter of the tank and physical ground water samples taken for off-site chemical analysis. However, such sampling is time-consuming and expensive. Moreover, because physically sampling is only a periodic action, it is unlikely to detect a leak or spill until significant damage has occurred.
Various instruments have also been proposed for non-physical and, in some instances, continuous monitoring of ground water and the like based on measurements, for example, of changes in dielectric properties of a sample or attenuation of light through a hydrocarbon-absorbing medium. Other systems have attempted to detect hydrocarbons by illuminating the sampling environment with light and measuring the fluorescence typically associated with hydrocarbons. However, these systems are typically expensive, sometimes inaccurate and often prone to maintenance problems.
It is an object of the present invention to provide improved, non-physical sensors and methods capable of either periodic or continuous monitoring of ground water, industrial facilities and commercial service stations for the presence of undesirable fluids in the environment.
It is another object of the present invention to provide an inexpensive, robust and compact sensor which can be placed, for example, in gasoline service station dispensor pans or sumps, or at other locations proximal to fuel tanks and other storage depots for hydrocarbon fuels or associated pipelines.